As many of you have seen there is a thread on the Modelbau MB339. It has lots of good information but I thought I would do a separate thread and chronicle my build. I have found many things that need attention so far on this little jet but I am convinced that she will be a good little everyday flyer when I am finished that I am determined to get it straightened out.

The very first thing I did was to clean up the glass work and removed excess material. Pic #1 shows me about to crop the aft wing opening area.

Pic #2 shows the front wing saddle bulkhead after I cleaned it up as well. Nice uniform radius of the glass looks much better.

Pic #3 shows the 1/8 inch ply doubler I made to laminate to the factory installed bulkhead. I will also make a 1/4 ply doubler to laminate to the rear of the same bulkhead. This will make the bulkhead 5/8 in thick....no way this will fail in flight!

Stay tuned, more to follow....

Subscribed. Do it Dave. Ya have a good start.

way to go Dave, Subscribed!, if weather permits I should Maiden mine tomorrow.

Good luck on the maiden! She is a true flyer and should not be much of a problem.

Ok, More of the build....I have been collecting pictures for a few days so it is gonna come fast and furious for now but will slow down as get caught up. The point of this build is to show that even a low buck model can be worked over until you have something that will serve you well.

Ok, Pic #1 shows the 1/8th ply doubler clamped in place.

Pic #2 shows it after the hysol has cured. Notice that the ply is now flush with the face of the glass work. I worked some hysol down in between the original bulkhead and the glass work filling any gap in that area.

Pic #3 shows the 1/4 inch doubler in place. now we have a 5/8ths thick bulkhead that is not going to fail, period.

Ok, question for any of you guys that have built the 339....did you use the Modelbau stock exhaust pipe? I have access to one and I am shocked at how heavy it is. As you may (or may not) know, the MB can be a very tail heavy bird requiring a bunch of nose ballast if you are not careful with the weight. Additionally, the stock pipe looks to be about 3 inches short. Fail all the way around! I have already contacted my buddy Tam and a new pipe is in the pipeline (pun intended).

Nonetheless, if you have a picture of your pipe install and would not mind sharing.... please do!

Now that the front bulkhead is squared away, its time to look at mounting the wing. Thats when I discovered the HORROR that is the motor mount! [:@]

The motor mount is/was installed so crooked that I had little choice but to remove it completely. I sat and thought about the pros and cons of removing it and reason over-ruled my being lazy and it was decided to yank it out. It took very little effort to remove this mount and the quality of the wood and glue used only served to reinforce my decision to remove and replace it.

So, how did we get from mounting the wing to the motor mount....well thats easy....the rear wing mount will tie into the motor mount soooo....the more you look the more you find, but I digress....

Picture #1 shows the original mount (sorry I had to use a picture over but its the only one I have of the original mount). You may be able to see the twist in the mount in the picture, maybe not but believe me its there.

Picture #2 shows some of the remaining glue that was used to fill the gaps between the wood bulkheads and the fuze....I am not sure what this glue is but they sure used a lot of it to fill gaps....

Picture #3 shows the new mounting system mocked up to see if I have what I need. The turbine mount is for a evoJet 90 and this is the turbine that will power this little jet.

Yo Dave.... subscribed. Looking forward to what you find and the subsequent corrections.

Rick

Dave my front retract strut that came with the kit broke on landing. What are you going to use? Just want to replace the strut. Any suggestions?

toto_sal...first off congrats on the maiden. Sounds like it was a success overall.

I am going to use Behotec Struts on my 339 so that would be my recommendation. Get hold of Peter at www.altecarerc.com and he will dial you in. He is a great guy and knows his stuff!

Ok...the work continues...

The rear bulkhead was fitted first and the remaining parts of the mount were located off of the rear bulkhead. Picture #1 shows the rear bulkhead in place.

I used my laser system to zero out the air frame and get the bulkhead in at 90 degrees. Picture #2 shows me getting the fuse lined up at zero degrees incidence.

Picture #3 shows the front bulkhead before it is installed. Making these bulkheads is a sand and fit kinda deal. What I do is I make a cardboard or poster board pattern by trimming and fitting and trimming and fitting.....after about an hour I have a pattern I can transfer to the plywood. Then I cut the plywood out staying slightly outside the lines of the pattern so I can sand it for a perfect fit. It takes time to get it right but once its done and glued in it will not move or fail. Because it takes time is exactly why it is not done from the factory on these cheaper models.

Continuing with the mount.

Picture #1 shows the front bulkhead in place with the two motor mounts and a third spacer to align the forward bulkhead. The actual motor mounts are not glued in place at this time. I will place them in position once the bulkheads have cured in place (over night).

Picture #2 shows this from a different view.

Picture #3 Shows the motor mounts in place. Again I used mu laser system to zero the air frame. I then shot a "line" from behind the jet up the tail pipe. Centering this line in the exhaust exit I was able to get the engine right on the thrust center line. Sweet!

Picture #4 is another view...if you look closely you will see nice clean hysol fillets....

Thanks Dave!

Dave a little more info on your laser system... thanks.

Rick

Rick, my laser unit is a Craftsman from Sears. It was about 90 bucks but is worth every penny. It is a self leveling unit and will shoot horizontal, vertical, or a cross-hair pattern. Dang handy for getting things lined up! I dont have the model number off hand but I believe it is the top of the line unit.

Updates...

I am at work tonight so I will not have pictures to go with my text, I have the pictures and will post them soon...

Worked continued and I am back to solving the original problem of mounting the wing. As I said previously, I have added two doublers to the bulkhead just forward of the wing opening, this is the bulkhead that carries the front of the wing. I have now added a 1/4 inch ply doubler to the inside of the wing where the mounting pins will hold the wing to the fuse. I feel that this will be more than enough to carry the wing loads in flight.

Next I made the wing hold down dowels. These are made from hollow carbon tubing with a center core of hardwood dowel. the outside diameter of the carbon dowel assembly is 1/2 inch and there will be two of them holding the wing in place. I seriously doubt that these will fail under any conditions.

Once I have the front of the wing pinned in place it will be time to start work on the rear hold down. I plan to use the same 4mm size bolts I have in my Flash so my field equipment requirements stay at a minimum.

On a side thought, I have read and read the Modelbau instructions on wing mounting and I still have no idea what they are wanting you to do for the front hold downs....no matter as I have moved past this part anyway.

Dave,

Thanks for the info on the laser.

Rick

Nice work Dave,

Did you by any chance save templates of the formers, etc you have made. I also have the MB339. Looks like that would save some effort in my construction effort (not started yet- still in the big box).

Thanks
John

My pleasure.




John, sadly I did not...I ment to but got caught up in the moment. Frankly, they are going to be a little different from machine to machine anyway....

hey Dave,
concerning the wing mount on the front end, its basically is what i would call a HE and SHE half moon, the former on the Fuse has the outer line shape of a half moon and on the wing you put the half moon that came in the wood parts bag, the piece that go on the wing has the same outer shape as the inner line on the former on the fuse so these mate perfect. what the manual tell you to do is place the wing on the fuse and then from the canopy access area mark exactly where the half moon on the wing would go and tact or glue it on the wing, after you remove the wing the you could put 2 small size bolts to help hold the half moon on to the wing so you can get a tight fit. it works nice and keeps the wing tight up against the fuse.

Who sells this kit. I don;t see it on Modelbau or Troybuilt's site.

Thanks,

Brian

Dave
very nice and clean work
awaiting for more pictures

best

I believe they have halted the kit due to building issuesthe customers are having and poor instructions, I think they may bring it back at a later time as a more complete ARF.

AM

OK Back to work!

Like I said, getting the wing mounted is what set everything in motion....

Ok, I decided that I want to use a pin and bolt system like I have on my CompARF Flash. So the first thing I needed to do was make some pins. I know some guys used wood dowels but I felt that they might not be strong enough so I built my own composite dowels using a carbon fiber tube and some hard wood dowel material. I then mated them up with a 1/4 ply circle that will back up the pins once they are installed.

Picture #1 & #2 Shows the pins

Picture #3 Shows the large holes in the forward bulkhead.

Pictures #4 & #5 show the hold down dowels installed in the wing.

Now it is time to start working on the rear hold down system. Like I said I will be using 4mm bolts to secure the wing in the rear. I have not started yet on this so I dont have any pictures....

Here is a picture of the evoJet 90 sitting on the mount!

Dave,
I had a friend visit me yesterday with his almost finished MB339. There seem to be some problems with the trusttube, it seems like it is too short (a few cm's), and the angle of it is off. The former in the back directs the end of the tube down into the fuse at the back, it seems like it it must be raised all the way up to the elevator wingtube, and even that might not be enough for it to clear the fuse at the back.
Have you tried to see how your thrusttube fits ?